1. Field of the Invention
This invention relates generally to a vibrating compressor, and more particularly to a vibrating compressor wherein ferrite magnets are employed as the permanent magent for applying magnetic field to an annular magnetic gap in which an electromagnetic coil driven by an electrical vibration system is disposed, and the operation thereof is maintained at the optimum condition at all times by ensuring uniform magnetic flux density in the annular magnetic gap and causing the electrical vibration system to positively vibrate in such a manner as to coincide with the intrinsic vibration period of a mechanical vibration system.
2. Description of the Prior Art
In general, the vibrating compressor has such a construction that a mechanical vibration system comprising a spring, and an electrical vibration system driving the mechanical vibration system are adapted to resonate with each other, based on the operating principle of a dynamic loudspeaker consisting of a magnet and a voice coil. In other words, the operation of the vibrating compressor can be compared to that of a synchronous motor.
Vibrating compressors of this type are now widely used in such applications as small-sized household refrigerators and mobile refrigerators used on board automobiles and boats.
Heretofore, alnico magnet has been widely used as a permanent magnet in this type of vibrating compressor. Because of its high cobalt content, the price of the alnico magnet has substantially increased as the price of cobalt has increased in recent years. As a result, ferrite magnet has attracted increasing attention as an alternative magnet available at lower cost. The present inventor and others have already proposed a vibrating compressor using the ferrite magnet (Japanese patent application No. 84108-1979). As suggested in the above patent application, the ferrite magnet, when used in such an application, is required to be of a flat shape with a larger crosssectional area and smaller thickness than the alnico magnet. As a result, when the ferrite magnet is used in place of the alnico magnet hitherto used in the vibrating compressor, due consideration must be given to the arrangement of the ferrite magnet. In some cases, the external shape of the conventional vibrating compressor may have to be changed unwantedly, or the outside diameter of the compressor may have to be increased. This requires the ferrite magnet to be formed into an arc shape or to be disposed along with the internal circumference of the external iron core.
When the arc-shaped ferrite magnet is used, as described above, the state of the annular magnetic gap in which the electromagnetic coil is reciprocated has important relations with the switching operation of the drive current fed to the electromagnetic coil. It is therefore desired that the relative position of the arc-shaped ferrite magnet and the reciprocating range of the electromagnetic coil be properly selected. It is also desired that magnetic flux density in the annular magnetic gap be maintained as uniform as possible.